The antimicrobial properties of silver have been utilized for centuries. For example, early Mediterranean cultures recognized that storing water in silver vessels rendered it potable. In the Middle Ages, silver nitrate was used for nervous disorders, epilepsy and for curing syphilis. In 1844, Crede, a German obstetrician, used a silver nitrate solution to eliminate blindness in newborns caused by post-partum infection. A silver nitrate solution was also used by von Behring in 1887 for the treatment of typhoid and anthrax. Other forms of silver such as coatings for the prevention of food spoilage and silver plates and foils for the surgical treatment of wounds and broken bones have also been used throughout the centuries.
It is believed that antimicrobial properties of silver may be provided by silver ions. As a result, efforts have been made in the prior art to produce compositions containing silver ions for use in providing antimicrobial properties. One challenge in producing such compositions is in providing compositions which are relatively “stable”, in that the silver ions will remain in ionic form in the compositions before use so that the silver ions are available during use to provide antimicrobial properties. Another challenge in producing such compositions is in providing methods of preparation of the compositions which are relatively economical.
U.S. Pat. No. 6,197,814 (Arata) discloses an aqueous disinfectant comprising an aqueous solution of silver citrate and citric acid produced by a process comprising electrolytically generating silver ions in a solution of citric acid and water, with the silver ions reacting with the citric acid to form electrolytically generated silver citrate having a concentration greater than the concentration of a non-electrolytically generated silver citrate within a similar or same solution of citric acid and water.
U.S. Pat. No. 6,838,095 (Newman et al) discloses a substantially non-colloidal solution made by combining ingredients comprising water, a source of free silver ions, and a substantially non-toxic, substantially thiol-free, substantially water-soluble complexing agent.
There remains a need for relatively economical methods for producing relatively stable aqueous solutions containing relatively high concentrations of silver ions. There also remains a need for relatively stable aqueous solutions containing relatively high concentrations of silver ions which may be used directly or diluted for use as antimicrobial compositions.